1. Field of the Invention
The present invention relates to a method for measuring the degree of edema which appears in one""s body and an apparatus using the same.
2. Prior Art
A swell caused by Intra-cellular or extra-cellular accumulation of interstitial fluid and lymph is called xe2x80x9cedemaxe2x80x9d. Appearing edema everywhere in a whole body may be realized as a symptom of diseases such as heart disease, kidney disease, liver disease, and such like. Therefore, measuring the degree of edema exactly is very useful in diagnosing or in monitoring patients"" condition.
The degree of edema, however, cannot be measured by ordinary people. Patients suffering from heart disease, kidney disease, liver disease or such like can monitor their weights regularly at home. The incremental weight, however, cannot be used as indicating the increment of water content in the body. The degree of edema, therefore, cannot be measured in terms of incremental weight. Specifically the body weight (Wt) represents a sum of weights of different body compositions, such as fat, fat free mass and total body water including intra-cellular water (ICW) and extra-cellular water (ECW). The weight of each body composition, however, cannot be separated from the weight of the body.
One object of the present invention is to provide a method of measuring the degree of edema with accuracy and easiness.
Another object of the present invention is to provide an apparatus which is capable of measuring the degree of edema with accuracy and easiness.
A method for measuring the degree of edema of a person according to the present invention comprises the steps of: putting at least two pairs of electrodes on different locations selected in the body of the person; supplying alternating current to one pair of electrodes; measuring voltage appearing between the other pair of electrodes; calculating impedance on the basis of the supplied alternating current and the measured voltage; and calculating an index value representing the degree of edema on the basis of the impedance.
Said alternating current may include a plurality of alternating current components of different frequencies, which are supplied one after another to said one pair of electrodes; voltage appearing between said the other pair of electrodes may be measured every time when an alternating current component of selected frequency is supplied; the impedance value may be calculated on the basis of each alternating current component and corresponding voltage; and the index value of edema may be calculated on the basis of the so calculated impedance values.
The index value of edema thus calculated may be a ratio of intra-cellular water to extra-cellular water or inversely, or a ratio of extra-cellular water to total body water or inversely.
An alternating current of single frequency may be supplied to said one pair of electrodes; and the index value of edema may be calculated on the basis of the phase difference between the alternating current and the voltage, and the resistance value calculated from the alternating current and the voltage.
An apparatus which is capable of measuring the degree of edema of a person according to the present invention comprises: at least two pairs of electrodes to be put on selected locations in the body of the person; an alternating current supplying device which supplies alternating current to one pair of electrodes; a voltage measuring device which measures the voltage appearing between the other pair of electrodes; and an arithmetic unit which calculates impedance on the basis of the supplied alternating current and the determined voltage, and calculates an index value representing the degree of edema on the basis of the so calculated impedance.
The alternating current supplying device may supply a plurality of alternating currents of different frequencies to said one pair of electrodes; and the voltage measuring device may measure the voltage appearing between said the other pair of electrodes every time when an alternating current of selected frequency is supplied, allowing the arithmetic unit to calculate the impedance values on the basis of each alternating current and corresponding voltage and to calculate the index value of edema on the basis of the so calculated impedance values.
The index value of edema thus calculated may be a ratio of intra-cellular water to extra-cellular water or inversely, or a ratio of extra-cellular water to total body water or inversely.
The edema measuring apparatus may further comprise a phase difference measuring device which measures the phase difference between the supplied alternating current and the measured voltage, whereby the arithmetic device may calculate the index value of edema on the basis of the phase difference and the resistance value calculated from the alternating current and the voltage provided that an alternating current of single frequency is supplied to said one pair of electrodes.
The edema measuring apparatus may further comprise an estimating device which determines what stage of edema the person has from the calculated index value of edema and other relevant data to be referred to.
Said estimating device may further determine whether the amount of food has been regulated well from the calculated index value of edema and other relevant data to be referred to.
Said other relevant data may be body weight or fat free mass of the person.
The edema measuring apparatus may further comprise an estimating device which determines what stage of edema the person has by comparing the calculated index value of edema with a reference value which represents the index value of edema in normal physical condition.
The edema measuring apparatus may further comprise an estimating device which determines what stage of edema the person has by comparing the present index value of edema with the average of the index values of edema already calculated.
The edema measuring apparatus may further comprise a display which shows the calculated index value of edema and/or the determined stage of edema the person has.
Said display may show a series of index values of edema already calculated, representing how the index value of edema has been varied.
Said display may show averages of index values of edema, each average representing the average of the index values calculated in each of 10 to 15 equi-divisions into which the length of time spanning from the outset to the latest measurement is divided.
The edema measuring apparatus may further comprise a communication device which transmits to other data processors at least one sort of information selected among measured voltage, measured phase difference, some derivations therefrom, calculated index value of edema, determined stage of edema the person has, and personal particulars.
Said communication device may receive the results of a given process executed on said information in said other data processors.
The edema measuring apparatus may further comprise a writing device which writes one sort of information selected among measured voltage, measured phase difference, some derivations therefrom, calculated index value of edema, determined stage of edema the person has, and personal particulars.